Electromagnetic energy has been widely used in medical applications for a very long time. With the advent of lasers, such applications have included tissue removal and shrinkage, tissue welding, etc.
The use of lasers for cosmetic surgery by dermatologists and plastic surgeons is expanding rapidly. Despite the fact that reimbursement for these procedures is often not covered under third-party payer health plans, other socio-economic factors seem to be driving the increased demand for these services. Such procedures include laser dosimetry to safely treat and remove vascular lesions (port wine stain and other red marks), benign pigmented lesions (brown marks) and in some cases, tattoo markings from skin surfaces. These procedures, though recently developed, are highly controllable and well known.
Collagen is the single most abundant animal protein in mammals, accounting for up to 30% of all proteins. The collagen molecule, after being secreted by the fibroblast cell, assembles into characteristic fibers responsible for the functional integrity of tissues making up most organs in the body. The skin is the largest organ of the body occupying the greatest surface area within the human body. As age advances and as a result of other noxious stimuli, such as the increased concentration of the ultraviolet part of the electromagnetic spectrum as radiated from the sun, structural integrity and elasticity of skin diminishes.
Facial rhytides (e.g., periorbital and perioral wrinkles produced by photodamage and/or aging) have previously been treated using a variety of modalities, including dermabrasion, chemabrasion (chemical peel), and CO.sub.2 laser skin resurfacing (LSR)--a technique in which pulsed or scanned CO.sub.2 laser light at 10.6 microns wavelength is used to ablate skin. All three modalities provoke a strong skin wound healing response that leads to wrinkle reduction--it is thought that the synthesis of new collagen essentially recontours the overlying skin surface.
Unwanted hair is a common dermatological and cosmetic problem, and can be caused by heredity, malignancy or endocrinological disease. Hair can be temporarily removed using wax epilation, depilatory creams and shaving. Permanent hair removal currently involves electrolysis, or the insertion of a current carrying needle into each hair follicle. Hair removal and the destruction of the generating follicle results from a traumatic episode within the hair follicle itself.
CO.sub.2 LSR has recently emerged as a widely used aesthetic surgical modality which may have advantages of improved reproducibility and control compared to dermabrasion and chemabrasion. However, CO.sub.2 LSR is often accompanied by complications such as persistent erythema, hyperpigmentation, hypopigmentation, scarring and infection. Patients also experience edema, drainage, and burning discomfort during, typically, the first few weeks after treatment. The present invention is directed toward treating facial rhytides using a new nonablative non-laser modality that may be effective in reducing both the severity of wrinkles and the incidence of morbidity presently associated with LSR.
Previous disclosures, such as U.S. Pat. No. 4,976,709 and No. 5,137,530 have described methods and apparatus for achieving controlled shrinkage of collagen tissue. These prior inventions have applications to collagen shrinkage in many parts of the body and describe specific references to the cosmetic and therapeutic contraction of collagen connective tissue within the skin. In the early 1980's it was found that by matching appropriate laser exposure parameters with these conditions, one had a novel process for the nondestructive thermal modification of collagen connective tissue within the human body to provide beneficial changes. The first clinical application of the process was for the non-destructive modification of the radius of curvature of the cornea of the eye to correct refractive errors, such as myopia, hyperopia, astigmatism and presbyopia. New studies of this process for the previously unobtainable tightening of the tympanic membrane or ear drum for one type of deafness have been made.
It is with this motivation that applications of collagen modulation have been driven. These techniques are intended to accomplish the same wrinkle removal without the usually attendant trauma and associated wound healing responses or inflammatory response. However, several drawbacks to the clinical use of medical lasers exist, including high initial costs of $50,000-150,000 and significant annual maintenance costs. Lasers are dangerous and require extensive training of personnel to avoid injury in the operating room. Furthermore, multi-wavelength operation with a typical laser system is impossible, and those systems offering multi-wavelength operation are more expensive and more complicated to operate. Finally, the efficiency of most laser systems is very low, and a very low amount of infrared energy is typically created within an operable wavelength domain, compared to the amount of energy required to drive the laser.
U.S. Pat. No. 5,595,568 issued Jan. 21, 1997 to Anderson et al. teaches permanent hair removal using optical pulses. The use of a medical laser is contemplated in conjunction with a rounded or flat probe for contacting the hairs to be removed and for transmitting heat through the skin layer to the follicles of the undesired hairs.
Utilization of non-laser electromagnetic energy for therapeutic and/or aesthetic treatment has been limited. One such use is taught in U.S. Pat. No. 5,344,418 issued Sep. 6, 1994 to Ghaffari, an optical system for treatment of vascular lesions. The invention teaches the use of a mercury vapor arc lamp with a wavelength domain of between 480 and 600 nanometers in conjunction with a passive cooling lens. The cooling lens is placed directly onto the surface of the skin, with cooling solution or fluid circulated on the opposite side of the lens, to prevent overheating of the surface layer of tissue.
Another invention utilizing non-coherent light is taught in U.S. Pat. No. 5,405,368 issued Apr. 11, 1995 to Eckhouse, which teaches a method and apparatus for therapeutic electromagnetic treatment. The device comprises a housing and an incoherent light source such as a flash lamp, operable to provide a pulsed light output for treatment, the device having a housing, reflector, light filter and a pulse forming circuit. The method of treatment includes steps of providing a high power, pulsed light output from a non-laser light source and directing the pulsed light output to a treatment area, with control of pulse width and filtration. The filament lamp used is gas filled and the domain of the output wavelength is within the visible range, i.e. 500-650 nanometers.
In both of the cited prior art documents, the emphasis is the use of non-laser energy for targeting blood vessels. They both strive to remove or reduce the infrared component of the light as it interferes with the treatment of blood vessels. Furthermore, neither gas filled filament lamps nor mercury-xenon arc lamps contain enough infrared output to be useful for the thermal modification of collagen.
Light transport in skin and other tissues is dominated by primary and secondary scattering events, rather than by optical absorption alone. Lask G, et al. Nonablative Laser Treatment of Facial Rhytides: SPIE Proc. 1997; 2970; xxx.
The concept of an "effective attenuation coefficient" .mu..sub.eff (in an exponential attenuation relation similar to Beer's law for absorption alone) has been used traditionally to approximate the light fluence .phi. (units: J/cm.sup.2) within a tissue in which scattering is important: EQU .phi.(z)=Aexp(.mu..sub.eff z) 1! EQU .mu..sub.eff ={3 .mu..sub.a .mu..sub.a +.mu..sub.s (1-g)!}.sup.1/2 2!
where
A is a constant, PA1 z is the depth (units: cm) within the tissue, PA1 .mu..sub.a is the absorption coefficient (units: cm.sup.-1), PA1 .mu..sub.s is the scattering coefficient (units: cm.sup.-1), and PA1 g is the scattering anisotropy (units: dimensionless). Welch A. J., van Gemert M. J. C. (editors). Introduction to medical applications: Optical-Thermal Response of Laser-Irradiated Tissue. (Plenum Press, New York 1995), pp. 609-618.
Light fluence .phi. is the energy (units: J) passing through a cross-sectional area (units: cm.sup.2) from all directions. It differs from the radiant exposure F (units: J/cm.sup.2) which we use in describing treatment parameters since F is the energy density directed onto the tissue surface from the light source. The fluence .phi. can be much larger than the radiant exposure F due to multiple scattering events--see FIG. 1 of Welch et al. When the tissue is highly scattering, on the average many photon scattering events occur before the photon is ultimately absorbed.
If the real light fluence distribution were represented by Equation 1!, the "effective optical absorption" as a function of depth z would mimic this exponential function and the "effective optical absorption coefficient" would be given by Equation 2!. However, the real light fluence distribution is more complicated than Equation 1! indicates and is best represented by a Monte Carlo modeling calculation which includes the effects of initial light distribution striking the tissue (e.g., collimated light at normal incidence, diffuse light at non-normal incidence, etc.), the changes of index of refraction at the air/tissue interface (and at any other interfaces within the tissue), absorption and scattering events within the tissue, and remittance from the tissue (by reflection at the air/tissue interface and by backscattering from within the tissue). Jacques S L, Wang L. Monte Carlo modeling of light transport in tissues: Optical-Thermal Response of Laser-Irradiated Tissue. (Plenum Press, New York, 1995), pp. 73-100.